From U.S. Pat. No. 4,539,184, a scrubber is known for removing sulfur compounds from a flue gas generated in a boiler combustion chamber. The scrubber is provided with a plurality of nozzles which spray a washing liquid containing fine-grained limestone (CaCO.sub.3) onto the flue gas so as to bind sulfur compounds from the flue gas which ascends from an inlet arranged below the nozzles to an outlet above the latter. At the bottom of the scrubber, a sump is formed by the descending liquid flow from which solids are discharged.
The sump is divided into two zones by a grate constituted by an array of oxygen ducts so as to define an upper oxidation zone and a lower reaction zone. The supply of limestone to the sump and thus to the washing liquid which is drawn off from the sump and conveyed to the nozzles is provided by a plurality of ducts located below the grate.
When the flue gas is introduced through the inlet and ascends towards the outlet, it is scrubbed in counterflow by the washing liquid which thus binds the sulfur compounds. Upon passing the oxidation zone, soluble sulfite is oxidized to sulfate which upon further supply of limestone to the reaction zone is converted to gypsum. The gypsum precipitates and can be discharged while the liquid forming the sump and containing limestone is returned to the nozzles.